This invention relates to a method of refining petroleum products, and in particular, to a method of refining petroleum products by the use of solvent extraction.
Solvent extraction used in petroleum refining is typically used in refining or upgrading various petroleum distillates and deasphalted oil. The presence of aromatic fractions is often undesirable, because such compounds often tend to oxidate or thermally degrade. With respect to diesel and other fuels, government regulations may limit the presence of aromatics. Aromatics also have poor viscometric properties, which is particularly important with respect to the production of lubricating or lube oils. For lube oils, the property of the lube oils that are most often used to indicate lube quality with regard to aromatics is the viscosity index (VI). Oils with high VI (95 or greater) are generally considered acceptable. Oils with a VI below 95 are usually considered inferior. Extracting the aromatics from these oils increases the VI of the oil. As presented herein, viscosity indices are determined pursuant to ASTM D2270.
Typical solvent extraction processes used in the refining of petroleum products and distillates utilize highly polar solvents. These solvents may include such things as phenol, furfural and NMP (N-methyl-pyrolidone), with NMP being the most recently developed solvent system presently in use for removing aromatic compounds. These solvents are highly selective for aromatics and various polar-compounds, but are less selective for saturated hydrocarbons, such as paraffins and cycloparaffins. The aromatic products removed during extraction can be used in fuels production or in specialized applications requiring high aromaticity.
The prior art solvent extraction techniques are usually carried out in a continuous flow process in which the solvent and petroleum product feed stream are maintained in the liquid phase and in countercurrent contact. The solvent is typically recovered, with the aromatics being removed, and the solvent is recycled back into the solvent feed stream. The solvent extraction is usually carried out at elevated temperatures that are well above ambient. Typically, these temperatures are from about 100xc2x0 F. to 250xc2x0 F. The elevated temperatures facilitate the flow of the petroleum products, which may contain wax, as well as increase the solubility of the aromatics in the solvent. At these elevated temperatures, however, saturates (i.e. paraffins and cycloparaffins), which may be either oils and/or waxes, may also be extracted by the solvent, resulting in lower yields of these products.
Crude petroleum and partially refined petroleum commonly contain waxes (usually paraffin waxes). These waxes crystallize or solidify at cooler temperatures. This is particularly notable with higher molecular weight n-paraffins, certain branched or iso-paraffins, and cycloparaffins. When petroleum is being refined for use as a lubricating oil, the presence of these materials, which crystallize within the range of temperatures for which the lubricating oils are used, is very deleterious. Thus, these materials are commonly removed in the refining process, which is oftentimes referred to as xe2x80x9cdewaxing.xe2x80x9d Therefore, after extraction, dewaxing of the petroleum products is usually carried out to improve the oil""s low temperature properties.
While conventional solvent refining or extraction techniques may be adequate for many applications, improvements are needed. In particular, extraction techniques that require less energy and processing equipment, and that result in higher purity and greater yields is highly desirous.
A method of refining a petroleum product is carried out by providing an unrefined petroleum product containing a first petroleum fraction and a second fraction to be separated, and wherein the first petroleum fraction has a melt point temperature. The unrefined petroleum product contains an amount of extractant, with the extractant having a freezing point temperature that is greater than the melt point of the first petroleum fraction.
The unrefined petroleum product is at a temperature at or above its pour point temperature so that the extractant is substantially liquefied. The first petroleum fraction is substantially dissolved within the liquefied extractant. A solvent is admixed with the unrefined petroleum product, with the second fraction being soluble within the solvent so that the second fraction is dissolved therein, and wherein the extractant is substantially insoluble within the solvent.
The mixture of unrefined petroleum product and solvent is brought to a temperature at or below the freezing point temperature of the extractant so that the extractant containing the dissolved first petroleum fraction is crystallized, while the solvent containing the dissolved second fraction remains in a liquid phase.
The crystallized extractant containing the dissolved first petroleum fraction is then separated from the liquid phase.
In another embodiment, a petroleum product is refined by providing an unrefined petroleum product containing a first petroleum fraction and a second fraction to be separated. The first petroleum fraction has a melt point temperature, and wherein the unrefined petroleum product contains an amount of extractant with a freezing point temperature that is greater than the melt point of the first petroleum fraction.
The unrefined petroleum product is at a temperature at or above its pour point temperature so that the extractant is substantially liquefied, with the first petroleum fraction being substantially dissolved within the liquefied extractant. A first solvent in which the second fraction is soluble is admixed with the unrefined petroleum product so that the second fraction is dissolved within the first solvent, with the extractant being substantially insoluble within the first solvent.
The mixture of unrefined petroleum product and first solvent is brought to a temperature at or below the freezing point temperature of the extractant so that the extractant containing the dissolved first petroleum fraction is crystallized, and the first solvent containing the dissolved second fraction is in a liquid phase. The crystallized extractant containing the dissolved first petroleum fraction is then separated from the liquid phase.
After this separation, a second solvent is admixed with the crystallized extractant and first petroleum fraction, with the first petroleum fraction being soluble within the second solvent. The first petroleum fraction is then separated from the crystallized extractant, and wherein the first petroleum fraction may be further separated from the second solvent.
In still another embodiment of the invention, a method of preparing lubricating oil from a petroleum product is provided. This is accomplished by providing a petroleum product containing a lubricating oil fraction and a second fraction to be separated from the lubricating oil. The lubricating oil fraction has a melt point temperature, and the petroleum product contains an amount of extractant, with the extractant having a freezing point temperature that is greater than the melt point of the lubricating oil fraction.
The petroleum product is at a temperature at or above its pour point temperature so that the extractant is substantially liquefied, with the lubricating oil fraction being substantially dissolved within the liquefied extractant. A first solvent in which the second fraction is soluble is then admixed with the petroleum product so that the second fraction is dissolved within the first solvent, with the extractant being substantially insoluble within the first solvent. The mixture of petroleum product and first solvent is brought to a temperature at or below the freezing point temperature of the extractant so that the extractant containing the dissolved lubricating oil fraction is crystallized and the first solvent containing the dissolved second fraction is in a liquid phase. The crystallized extractant containing the dissolved lubricating oil fraction is then separated from the liquid phase.
A second solvent is then admixed with the crystallized extractant and lubricating oil fraction, with the lubricating oil fraction being soluble within the second solvent so that the lubricating oil fraction is dissolved within the second solvent. The lubricating oil fraction and second solvent is then separated from the crystallized extractant. The lubricating oil fraction is then separated from the second solvent to provide a lubricating oil.